1. Name the type of white blood cell involved in the non-specific immune response.
Answer
Phagocyte.
2. Name the cell that is able to stimulate both the humoral and cell-mediated response.
Answer
Helper T cell.
3. Describe the role played by helper T cells that leads to agglutination of pathogens.
Answer
A specific helper T cell with the matching receptor is stimulated by an antigen-presenting cell. The helper T cell then stimulates a specific B cell with a complementary membrane-bound antibody to the antigen. The B cell undergoes clonal selection by mitosis, dividing into many plasma cells. These plasma cells secrete antibodies that cause agglutination.
4. The figure below shows one method used to treat cancer. It involves the use of monoclonal antibodies in a technique called ADEPT (antibody-directed enzyme prodrug therapy). The monoclonal antibody has an enzyme attached. The antibody binds to antigens on the cancer cell. This is shown as stage A. In stage B, an inactive prodrug is given to the patient. The enzyme converts the prodrug to an active cytotoxic drug that enters the cancer cell. There is a time delay between stage A and B to allow any antibodies that have not bound to cancer cells to be broken down so that they are no longer present in the blood. Explain why.
Answer
Prodrug could bind to antibodies in blood. The active drug is not delivered to cancer cells and could destroy healthy cells.
5. The monoclonal antibody used in the process above is produced using mouse cells. Suggest a possible disadvantage of this for the cancer patient.
Answer
The mouse antibody is recognized as a foreign antigen. The human immune system mounts a response, and memory cells are produced. As a result, the monoclonal antibody cannot be used again because it will be destroyed by the memory cells and the immune system.
6. The figure below shows the Human Immunodeficiency Virus (HIV). Name structures A and B. Describe the importance of enzyme C.
Answer
A = capsid,
7. People who are infected with HIV have antibodies against the virus in their blood. The figure below shows how one kind of test works. Explain why it is important that the well is washed between stages B and C.
Answer
To ensure antibodies have bound to antigen and unbound antibodies are washed away.
8. Explain why it is important that the well is washed between stages C and D.
Answer
This ensures that the antibody with the enzyme has bound. If the well is not washed, the enzyme may remain present and give a false positive result.
9. Explain why it is necessary to use a secondary antibody with an enzyme and a substrate that changes colour in the presence of the enzyme.
Answer
The colour change is produced to create a visible difference, since antibodies and antigens are too small to be seen.
10. There will be no colour change if a patient does not have HIV antibodies in their blood. Explain why.
Answer
There are no antibodies to bind to the antigen. Therefore, the secondary antibody does not bind, and no enzyme is present to change the colour of the well.